The present application relates to a system (10, 60) for treating a part of a body of a person to be treated. The system includes a treating device (20, 70) having a treating unit (22, 72) and a reference member (40, 80) adapted to be mountable to a person in fixed relationship to a part of the body. The treating device (20, 70) has a first motion identifier (28) configured to generate information indicative of the acceleration and/or angular orientation of the treating device (20, 70). The reference member (40, 80) has a second motion identifier (48) configured to generate information indicative of the acceleration and/or angular orientation of the reference member (40, 80). A controller (27, 47) is adapted to produce information indicative of the trajectory and/or orientation of the treating unit (22, 72) relative to the part of the body to be treated based on the information provided by the first and second motion identifiers (28, 48). The present application also relates to a treating device (20, 70) and a method of treating a part of a body of a person to be treated.
